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CAIE A-Level Physics 18.5.3 Point-Charge Potential

Practise calculating and rearranging V = Q/(4 pi epsilon0 r) for point charges, adding signed potentials and interpreting inverse-distance variation.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • calculate electric potential due to a point charge using V = Q/(4πε₀r)
  • rearrange the relationship to determine charge, distance or potential and use consistent units
  • interpret the sign and inverse-distance variation of point-charge potential

18.5.3—V = Q / (4πε0 r) for the electric potential in the field due to a point question 1

[Maximum number: 2]

Two small solid metal spheres A and B have equal radii and are in a vacuum. Their centres are 15 cm apart.
Sphere A has charge +3.0 pC and sphere B has charge +12 pC . The arrangement is illustrated in Fig. 5.1.

Fig. 5.1

Fig. 5.1

Point P lies on the line joining the centres of the spheres and is a distance of 5.0 cm from the centre of sphere A .

Calculate the electric potential at point P.

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